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BITUMINOUS CONSTRUCTION

THE HIGHWAY INDUSTRY IS RELUCTANT TO ABANDON TRADITIONAL METHODS AND SPECIFICATIONS AND ADOPT STATISTICALLY DERIVED TOLERANCES, EVEN THOUGH THE NEW LARGER TOLERANCES ARE DEMONSTRABLY SOUND. FOUR STEPS ARE NECESSARY TO IMPLEMENT STATISTICAL SPECIFICATIONS: (1) ESTABLISHMENT OF A REALISTIC VARIABILITY; (2) USE OF THE VARIABILITY TO ESTABLISH REALISTIC TOLERANCES; (3) SIMULATION OF THE NEW SPECIFICATION; AND (4) USE OF THE NEW SPECIFICATION AS THE BASIS OF ACCEPTANCE IN A CONTRACT. ONLY FOUR STATES HAVE REACHED THE LAST STEP. THE TYPICAL COMPONENTS OF STATISTICAL SPECIFICATIONS ARE: LOT SIZE, SAMPLE, NUMBER, ACCEPTANCE OF CENTRAL TENDENCY, ACCEPTANCE OF VARIABILITY, OTHER ACCEPTANCE CRITERIA (PERCENT DEFECTIVE PRODUCT QUALITY INDEX, SEQUENTIAL ANALYSIS LIMITS), ADJUSTMENT OF BID PRICE, CONTROL CHARTS, AND RETESTING AND REFEREE PROCEDURES. BECAUSE OF THEIR CLARITY AND DEFENSIBILITY, STATISTICAL SPECIFICATIONS SOLVE MANY OF THE PROBLEMS CAUSED BY INDEFINITE AND ARBITRARY SPECIFICATIONS. HOWEVER, THERE IS A LACK OF STATISTICAL TRAINING AMONG ENGINEERS, WHICH MUST BE REMEDIED BEFORE STATISTICAL SPECIFICATIONS CAN BE IMPLEMENTED.